In an existing Long Term Evolution (LTE) system, when a UE is handed over between cells, a random access procedure is used to acquire uplink synchronization with a target cell.
In FIG. 1, when a source cell receives a Radio Resource Control (RRC) measurement report (Measurement Reports) from the UE, a Handover Request message is sent to a target cell, and after receiving a Handover Request ACK (Handover Request Confirm) message returned from the target cell, a Handover Command is sent to the UE. According to the Handover Command, the UE begins to be detached from the source cell, and is synchronized with the target cell. At this time, the UE completes the uplink synchronization with the target cell through the random access procedure, and obtains an Uplink Grant (UL Grant) of the target cell, and furthermore, the UE sends a Handover Complete message on a scheduling resource that is corresponding to the obtained UL Grant. The target cell performs a corresponding Hybrid Automatic Repeat Request (HARQ) ACK after correctly receiving a data block of the Handover Complete message, and meanwhile, the target cell sends a Handover Complete indication to the source cell to confirm that the handover is complete, where the Handover Complete indication may be a UE context release message.
During the implementation of the present invention, the inventor researches and finds that during a handover, performing a random access procedure of uplink synchronization causes a longer delay.